Convergent evolution of pollen transport mode in two distantly related genera (: and ) Zachary M. Portman, Vincent J. Tepedino

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Zachary M. Portman, Vincent J. Tepedino. Convergent evolution of pollen transport mode in two distantly related bee genera (Hymenoptera: Andrenidae and Melittidae). Apidologie, Springer Verlag, 2017, 48 (4), pp.461-472. ￿10.1007/s13592-016-0489-8￿. ￿hal-01702524￿

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HAL is a multi-disciplinary open access L’archive ouverte pluridisciplinaire HAL, est archive for the deposit and dissemination of sci- destinée au dépôt et à la diffusion de documents entific research documents, whether they are pub- scientifiques de niveau recherche, publiés ou non, lished or not. The documents may come from émanant des établissements d’enseignement et de teaching and research institutions in France or recherche français ou étrangers, des laboratoires abroad, or from public or private research centers. publics ou privés. Apidologie (2017) 48:461–472 Original article * INRA, DIB and Springer-Verlag France, 2017 DOI: 10.1007/s13592-016-0489-8

Convergent evolution of pollen transport mode in two distantly related bee genera (Hymenoptera: Andrenidae and Melittidae)

Zachary M. PORTMAN, Vincent J. TEPEDINO

Department of Biology, Utah State University, Logan, UT 84322-5305, USA

Received 31 July 2016 – Revised 11 December 2016 – Accepted 28 December 2016

Abstract – Purposeful transport of pollen represents a key innovation in the evolution of from predatory wasps. Most bees transport pollen on specialized hairs on the hind legs or ventral metasoma in one of three ways: moist, dry, or Bglazed,^ which combines dry and moist transport. The evolutionary pathway among these three transport modes is unclear, though dry transport has been hypothesized to be ancestral. We address this hypothesis using museum specimens and published records of the bee genera (Andrenidae) and Hesperapis (Melittidae), two distantly related groups whose pollen transport modes appear to have converged. Most species in both genera transport moistened pollen; glazed and dry transport are limited to derived clades of specialists on floral hosts in and Onagraceae, with specialization on Asteraceae associated with more elaborate scopal hairs. The associations between transport mode, host , and hair type may be due to the sticky pollenkitt of asteraceous pollen grains and the viscin threads of Onagraceae pollen, which provide alternates to the binding properties of nectar. These findings suggest that the hypothesis that dry transport is ancestral in bees should be reexamined.

Apoidea / glaze / Hesperapis / Perdita / scopae

1. INTRODUCTION 2007). Transport on the hind legs is facilitated by structural elaborations, mostly of the tibia and Female bees collect pollen at flowers and trans- basitarsus, to include either hair brushes (scopae) port it to the nest where it serves as the primary or flattened plates (corbiculae). protein source for their progeny. Although past Pollen is packed on the hind legs and research has explored the various adaptations of transported in one of three modes: moistened with bees to gather pollen (e.g., Thorp 1979; Müller nectar or oils (Figure 1a, b), dry (Figure 2c, d), or 1996a, b; Müller and Bansac 2004), fewer studies Bglazed,^ a combination of dry and moist collec- have addressed how pollen is transported to the tion (Figure 1c, d). A glazed pollen load is initially nest. Although a few bee taxa transport pollen packed dry and is then capped with nectar during internally in the crop, most transport it either on the latter part of the foraging trip (Thorp 2000; the ventral metasoma (e.g., most Megachilidae) or, Eickwort et al. 1986; Norden et al. 1992). Al- more commonly, on the hind legs (Michener though most bee species transport dry pollen, five of the seven bee families also contain genera with Electronic supplementary material The online version of species that transport either moistened or glazed this article (doi:10.1007/s13592-016-0489-8) contains pollen: Andrenidae, Apidae, Halictidae, supplementary material, which is available to authorized Melittidae, and Stenotritidae (Malyshev 1936; users. Houston and Thorp 1984; Westerkamp 1996; Corresponding author: Z. Portman, Thorp 2000; Michener 2007). [email protected] The evolutionary sequence of external pollen Manuscript editor: James Nieh transport among the three modes is presently 462 Z.M. Portman and V.J. Tepedino

Fig. 1 Lateral views of moist and glazed transport. a Moist transport of Loasaceae pollen by Perdita perplexa Timberlake on simple hairs. b Moist transport of Asteraceae pollen by P. n. sp. 2 aff. laticincta on simple hairs. c Glazed (25% dry) transport of Asteraceae pollen by Hesperapis hurdi Timberlake on branched hairs. d Glazed (80% dry) transport of Asteraceae pollen by P. albonotata Timberlake on corkscrew-shaped hairs.

unsettled. Traditionally, primitive bees were have hypothesized that plumose hairs originated thought to transport pollen internally in the crop as an adaptation for temperature and water regu- (Malyshev 1936; Jander 1976; Michener et al. lation rather than pollen transport (Engel 2001, 1978; Michener 1979). More recent hypotheses Michener 2007). The paucity of bees in the fossil propose that primitive bees transported pollen dry record (Michez et al. 2012) offers little additional on plumose hairs that covered most of the body help in disentangling the evolution of pollen trans- (Roberts and Vallespir 1978; Radchenko and port or of hair traits. Pesenko 1996; Michener 2007). This hypothesis Bee genera that contain some species that trans- is presumably supported by the branched body port moist pollen and others that transport pollen hairs and plumose hindleg hairs found on the dry are particularly apt to shed light on the evolu- oldest known bee fossil (∼100 Myr), a single male tionary sequence of pollen transport modes espe- Melittosphex burmensis Danforth and Poinar cially when phylogenies are available for compar- (Danforth and Poinar 2011). Alternatively, others ison. Two examples are the genera Perdita

Fig. 2 Dry transport of Onagraceae pollen. a Sparse, simple scopal hairs of P. pallida Timberlake. b Denser and longer scopal hairs of Perdita vespertina Griswold & Miller. c Dry transport Onagraceae pollen on P. pa ll id a . d Closeup of c showing viscin threads binding pollen together. Evolution of pollen transport 463

(Andrenidae) and Hesperapis (Melittidae) specialists). Since both dry and moist transport are (Timberlake 1954;Stage1966), which are distant- exhibited by diverse generalist and specialist pol- ly related (Cardinal and Danforth 2013; Hedtke len foragers on the same host, it suggests that et al. 2013), yet have several similarities: They are additional factors such as scopal hair characteris- restricted to North America (Michener 2007; tics or evolutionary limitations might be germane. Michez et al. 2007), are most diverse in the arid It has been previously suggested that the struc- west (Michener 2007), and are comprised almost ture, density, and distribution of the scopae corre- exclusively of oligoleges, i.e., species which use spond to pollen properties. The scopal hairs asso- pollen from a small set of related floral hosts ciated with dry transport often reflect the size and (Linsley 1958;Stage1966; Eickwort and ornamentation of the pollen specialized on Ginsberg 1980;Caneetal.1996; Minckley et al. (Linsley 1958;Thorp1979). Examples include 2013). A recent partial phylogeny is available for long simple hairs on bees specialized on Perdita (Danforth 1996) and preliminary ones are Onagraceae (Michener 1944; Linsley et al. 1963; available for Hesperapis (Stage 1966; Michez Thorp 1969, 1979); hair brushes of long, simple, et al. 2009). curved hairs on bees specialized on Cucurbitaceae At present, the incidence of Perdita species (Hurd and Linsley 1964); and dense, finely plu- that transport moist, dry, or glazed pollen loads mose, or branched scopal hairs on bees special- is unknown. Although many are thought to trans- ized on small, spiny Asteraceae pollen (Linsley port a pollen mass that has been continuously 1958; Linsley and MacSwain 1958; Moldenke moistened with nectar as it is packed onto the hind 1979). Alternatively, other studies suggest that tibia (Timberlake 1954; Thorp 1979; Michener the simple scopal hairs of moist transporters are 2007;Neff2008), the genus is large (>630 adaptable to holding many pollen types (Roberts species, Portman et al. 2016) and the transport and Vallespir 1978; Thorp 1979, 2000; Michener modes of only seven species have been studied 2007). In Perdita ,therearecleardifferencesinthe in detail. Of these, six are moist transporters and structure of the scopal hairs between species that one transports glazed pollen (Online Resource 1: transport moist or glazed pollen; species that Table SI). Species that Bglaze^ their pollen loads transport glazed pollen typically have longer, are thought to be confined to one monophyletic denser, and more structurally complex scopal section of seven subgenera (Danforth 1996; hairs (Timberlake 1954; Danforth 1996). Timberlake 1954; Michener 2007). The pollen Our objectives here are threefold: (1) expand transport mode of most Hesperapis (∼40 species, our knowledge of the distribution of dry, moist, Cane et al. 1996) species is also poorly known; and glazed pollen transport in Perdita and only three, all moist-transporters, have been in- Hesperapis , (2) determine if pollen transport vestigated in depth (Online Resource 1: Table SI). mode is associated with specialization on particu- At least two salient factors may influence pol- lar floral hosts or pollen types, and (3) uncover len transport mode: host plant choice, scopal hair associations between scopal hair types and pollen morphology and distribution, or an interaction of transport mode. We then use extant though incho- the two. Thorp (1979) proposed that moist pollen ate phylogenies to derive systematic hypotheses transport would be particularly advantageous to which address the origin and evolution of pollen generalist pollen foraging species because moist- transport. ening facilitates the agglutination of pollen of diverse shapes and sizes (see also Vaissière and 2. METHODS Vinson 1994). Paradoxically, however, many of the species that transport moistened pollen are Specimens in the genera Perdita and oligolectic (Thorp 1979 ). In addition, there are Hesperapis were examined from the USDA Pol- many examples of host plant pollen being collect- linating Research Unit (PIRU) collection in ed by different bee species that employ contrast- Logan, UT and the Entomology Research Muse- ing transport modes (e.g., Hurd and Linsley 1975, um, University of California, Riverside, CA using Larrea specialists; Hurd et al. 1980, Helianthus a Leica M125 or MZ12 stereomicroscope with a 464 Z.M. Portman and V.J. Tepedino

Techniquip ProLine 80 LED ring light. A subset we did not survey specimens with signs of wetting of specimens was further examined using a Quan- on other parts of the body such as matted hairs. ta FEG 650 Scanning Electron Microscope to We surveyed a representative subset of species confirm or refine findings on the distribution and from every subgenus and major species group of morphology of scopal hairs and pollen grains. the target genera (Online Resource 2: Table SII). Pollen transport mode was classified into three Multiple specimens of each species from varying groups: moist (Figure 1a, b, entire pollen load collection locations and times were surveyed moistened), dry (Figure 2c, d, no moistening whenever possible (Online Resource 1: detected), or glazed (Figure 1c, d, an initial layer Table SI). An attempt was made to survey species of dry pollen covered by a layer of moistened that collectively specialize on a wide range of pollen). In bees that transport glazed pollen, we floral hosts. Particular attention was paid to bee estimated the proportion of the pollen load on the groups thought to contain species that transport tibia and basitarsus that was dry. Some species dry or glazed pollen; these groups had all avail- were represented only by specimens with partially able species surveyed. Records for four species filled dry pollen loads, making it impossible to not represented in the PIRU collection by speci- distinguish between dry and glazed transport. mens with pollen were compiled from the litera- These specimens were classified as transporting ture (Online Resource 1: Table SI). initially dry pollen. Floral specialization of Perdita and We categorized scopal hair type by the location Hesperapis species was compiled from various of hairs on different areas of the hind legs, hair published sources and visitation records in the length, hair morphology, and the presence of pol- PIRU database (US NPID 2016; Online len in those hairs. Although hair density and Resource, Table SI). Lastly, scopal pollen of rep- length are continuous rather than discrete charac- resentative specimens was compared to pollen on ters, we were able to confidently place them into slides prepared from previous studies in Clark discrete categories. Hair density was estimated County, NV, and Colorado (Tepedino et al. based on the space between scopal hairs and was 1999;Griswoldetal.2006). Morphological ter- classified into three groups: sparse, medium, or minology and taxonomic classification of Perdita dense, based on whether the integument was follow Michener (2007), and taxonomic classifi- clearly visible, partially obscured, or fully ob- cation of Hesperapis follows Michez et al. (2007) scured, respectively. Hair length was classified and includes the unnamed species from Stage as short, medium, or long based on whether the (1966) and Michener (1981). hairs were less than 2× the maximum width of the hind tibia, between 2 and 3×, or greater than 3×, 3. RESULTS respectively. We also classified the associated pollen-transporting hairs on the anterior face of The vast majority of both Perdita and the hind tibia as either simple, branched, wavy, or Hesperapis species surveyed are oligolectic, spe- corkscrew-shaped (Figure 3). cializing on floral hosts in one of 21 and 9 plant We used two steps to determine whether pollen families, respectively (Table I). Most species in in the scopae was moist or dry: a pollen load was both genera transported pollen that had been uni- deemed moist-packed if it was compact and ex- formly moistened with nectar (94 of 136 species tended beyond the scopal hairs. To further confirm of Perdita ; 11 of 17 species of Hesperapis ). Dry the moist-packed designation, an insect pin was or glazed pollen transport only occurred in species used to poke the pollen mass. Moistened pollen in of both genera that specialized on Asteraceae or museum specimens hardens into an impervious Onagraceae pollen. mass that resists Bpoking,^ whereas dry pollen offers no resistance and is readily penetrated. Be- 3.1. Glazed or dry pollen transport causepolleninthescopaecanbewettedpassively when bees are collected in pan traps, malaise Forty-two species of Perdita transported either traps, or when bees regurgitate nectar in kill jars, glazed or dry pollen: 24 glazed, 15 dry at least Evolution of pollen transport 465

Fig. 3 Optical and SEM examples of the different hair types. a and b Simple hairs on moist-transporting Perdita koebelei Timberlake. c and d Branched hairs on P. as te ri s Cockerell. e and f Wavy hairs on P. lingualis Cockerell and P. albovittata Cockerell, respectively. g and h Corkscrew-shaped hairs on P. moabensis Timberlake. All SEM scale bars = 50 μm

initially, and 3 dry (Table I;OnlineResource1: Resource 2: Fig. S2; Timberlake 1954; Danforth Table SI). Thirty-eight of those 42 species special- 1996). In contrast, the 18 surveyed species that ize on Asteraceae hosts with the proportion of dry transported entirely moist Asteraceae pollen are pollen ranging from 25 to 80%. Bees that glaze scattered across at least four unrelated subgenera their pollen loads do not entirely cap the basal and species groups: subgenus Pygoperdita (2) layer of dry pollen; instead, moistened pollen is and the species groups Octomaculata (9), always added at a similar location on the anterior Ventralis (2), and Zonalis (5) within subgenus face of the hind tibia and only partially covers the Perdita s. s. (OnlineResource2,TableSII). All dry pollen (e.g., Figure 1c, d). Of the four species of the Perdita species specialized on Onagraceae specialized on Onagraceae hosts, three are in the single monophyletic subgenus transported dry pollen loads and one transported Xerophasma (Griswold and Miller 2010). pollen dry at least initially. No Hesperapis transported entirely dry pollen: The distribution of glazed and dry pollen trans- of six species that transported glazed pollen, five port follows a clear phylogenetic pattern. Al- specialized on hosts in Asteraceae and one on an though Perdita species in at least 11 subgenera Onagraceae host (Table I; Online Resource and species groups are specialized on Asteraceae 1:Table SI). The proportion of dry pollen in glazed pollen (Online Resource 2: Table SII), the species loads ranged from 10 to 25% for Asteraceae spe- that transport glazed pollen fall into a single cialists and 50% for the lone Onagraceae special- monophyletic group of seven subgenera (Online ist. As with Perdita , moist pollen was added by 466 Z.M. Portman and V.J. Tepedino

Table I. The number of Perdita and Hesperapis species examined, categorized by host plant family and mode of pollen transport

Host plant family Transport mode

Perdita Hesperapis

M G DDISUMMGDDISUM

Amaranthaceae 1 1 Aquifoliaceae 1 1 Asparagaceae 1 1 Asteraceae 18 24 14 56 1 5 6 Boraginaceae 7 7 Brassicaceae 3 3 Cleomaceae 2 2 Euphorbiaceae 7 7 Fabaceae 11 11 1 1 Fabaceae and/or Zygophyllaceae 1 1 1 1 Hydrophyllaceae 1 1 Lamiaceae 2 2 Liliaceae 3 3 Loasaceae 4 4 2 2 Malvaceae 4 4 1 1 Onagraceae 3 1 4 1 1 Papaveraceae 4 4 Polemoniaceae 3 3 2 2 Polygonaceae 4 4 Rosaceae 3 3 1 1 Salicaceae 2 2 Solanaceae 6 6 Unknown 2 2 Zygophyllaceae 5 5 1 1 Total 94 24 3 15 136 11 6 17

M moist, G glazed, D dry, DI dry initially

Hesperapis females atop dry pollen only on the one species in the Sphaeralceae Group which trans- anterior face of the hind tibia and did not evenly ports Fabaceae pollen on minutely branched hairs. cap the dry pollen in the scopa. Otherwise, the hairs of the moist-transporting Perdita species are remarkably uniform, despite 3.2. Hair types transporting pollen of 20 diverse plant families (Online Resource 2: Table SII). Similarly, all 11 Pollen transport mode is associated with partic- species of Hesperapis that transport moistened pol- ular hair types in both Perdita and Hesperapis len have simple scopal hairs that appear to act as (Online Resource 2: Table SII; Figure 3). Ninety- generalized anchors for masses of agglutinated pol- three of 94 Perdita species that transport moistened len; these species specialize on collecting pollen pollen have simple scopal hairs. The exception is from nine disparate plant families. Evolution of pollen transport 467

In both Perdita and Hesperapis , glazed trans- face of the hind trochanter (Figure S1_B). The port of Asteraceae pollen is associated with denser morphology of the scopal hairs on the posterior and longer hairs compared to those that transport face of the tibia matches the hairs on the anterior moistened pollen (Online Resources: Tables SII, face, but the hairs on the femur and trochanter are SI). Perdita species that transport glazed always branched, regardless of the hair type on the Asteraceae pollen are also more likely to have tibia. Similar to Perdita ,allfourHesperapis spe- diverse scopal hair types, including simple, cies that transport glazed Asteraceae pollen have branched, wavy, or corkscrew-shaped (Figure 3); scopal hairs on the posterior face of the hind tibia, the most common scopal hair type is wavy (24 and three also have branched hairs on the femur species, 3 subgenera), followed by branched (10 and trochanter of the hind legs. However, the hairs species, 2 subgenera), corkscrew-shaped (3 spe- on the femur and trochanter of those Hesperapis cies, 2 subgenera), and simple (1 species) are relatively sparse and short compared to (Table SII). A 2 × 2 contingency table analysis Perdita and appear to transport only a dusting of (Maxwell 1961) of hair type (simple vs. elaborate) pollen, if any. In both Perdita and Hesperapis by transport mode (moist vs. glazed or dry) for species that transport glazed pollen, the expanded Perdita was highly significant (X 2 =109.2,df=1, scopal hairs on the trochanter, femur, and posteri- P << 0.0001): moist and simple hairs are highly or face of the hind tibia always transport entirely associated as are elaborate hairs and glazed or dry dry pollen; they are never capped with moistened transport (Online Resource 2: Table SIII). The pollen like the scopal hairs on the anterior face of Hesperapis species that transport glazed the tibia. Asteraceae pollen have either branched (4 species) The differences in the distribution of the scopal or simple (1 species) hairs (Table SII). hairs of bees that collect dry or glazed Onagraceae In both Perdita and Hesperapis , dry or glazed pollen are relatively minimal compared to those transport of Onagraceae pollen is associated with that transport moist pollen. All of the Perdita simple scopal hairs, although they are sometimes species that transport dry Onagraceae pollen have longer and denser than the scopal hairs of species an expanded distribution of scopal hairs only on that transport moistened pollen. Of the four sur- the posterior face of the hind tibia. Similarly, the veyed Perdita species which are Onagraceae spe- one species of Hesperapis that transported moist- cialists, two have scopal hairs whose type, length, capped Onagraceae pollen has simple and sparse and spacing are similar to moist-transporting scopal hairs on the posterior face of the hind tibia, Perdita species (Figure 2a), although the other though they are shorter than the hairs on the two species have longer and denser scopal hairs anterior face. (Figure 2b).

3.3. Hair distribution 4. DISCUSSION

The distribution of pollen-transporting hairs on The distantly related bee genera Perdita abee’s hind legs also differs between moist and (Andrenidae) and Hesperapis (Melittidae) dry or glazed pollen collectors, with scopal hairs (Cardinal and Danforth 2013; Hedtke et al. of species that transport moist pollen tending to 2013) display convergent (Arendt and Reznick cover a smaller surface area than species that 2008) evolutionary patterns of pollen transport. transport dry or glazed pollen. For example, the In both genera, most species examined transport scopal hairs of Perdita that transport moist pollen completely moistened pollen loads and a minority are located only on the anterior face of the hind transport either glazed or dry pollen loads. Those tibia and basitarsus. In contrast, all Perdita exam- that transport glazed or dry pollen specialize only ined that transport dry or glazed Asteraceae pollen on floral hosts in the families Asteraceae and have pollen-transporting hairs that also cover the Onagraceae, even though Perdita and lateral and posterior face of the hind tibia, the Hesperapis contain species that specialize on 21 anterior side of the hind femur, and the anterior and 9 plant families, respectively (Table I). 468 Z.M. Portman and V.J. Tepedino

Available evidence suggests that moist pollen The association of Asteraceae or Onagraceae transport is ancestral in both genera and that the pollen with glazed or dry pollen transport, and most probable evolutionary pathway is from moist more elaborate scopal hairs may be due to the to glazed or moist to dry. This hypothesis is sup- physical properties of the pollen grains, particu- ported in Perdita by the near ubiquity of moist larly those which may confer an alternative bind- transport in the subfamily (Rozen ing mode. Onagraceae pollen in particular has 1967;Michener2007), of which Perdita is a mem- sticky viscin threads that attach the pollen grains ber,andbyDanforth’s(1996) morphological phy- together and to the scopal hairs of bees (Linsley logeny for Perdita which shows that glazed and/or 1958; Roberts and Vallespir 1978;Hesse1981). A dry pollen transport is limited to two derived clades similar binding function may be provided by the (Online Resource 2: Fig. S2). In addition, copious pollenkitt and echinate projections of subgenera that transport the highest proportion of Asteraceae pollen. Pollen with copious pollenkitt, dry pollen fall in the more derived clades (Danforth such as Asteraceae and Malvaceae, is more adhe- 1996). The hypothesis that moist transport is basal sive than other pollen types and readily attaches in Hesperapis is supported by Stage’s(1966)in- passively to foragers in large amounts (Allard choate morphological phylogeny as well as the 1910;Parker1981 ; Buchmann and Shipman seven species of Hesperapis included in the mo- 1990;NeffandSimpson1997;Thorp2000; lecular phylogeny of Michez et al. (2009). Both Goulson et al. 2005). Pollenkitt’s adhesive prop- phylogenies have the glazed and dry-transporting erties may also be enhanced by pollen sculpturing species limited to derived clades, with glazed trans- because spiny or echinate pollen grains can pro- port of Asteraceae and dry transport of Onagraceae mote adhesion to other pollen grains or other likely arising in separate derived clades in Perdita . surfaces by increasing the available surface area Overall, the patterns in both genera suggest that with which pollenkitt may interact (Roberts and they are responding to similar selective pressures. Vallespir 1978; Lin et al. 2013). Pollen spines may Evidence also suggests that the evolution of also enhance the electrostatic binding potential of glazed or dry transport in these genera was initi- pollen (Chaloner 1986; Hesse 2000). Overall, de- ated by a host switch to either Asteraceae or spite being unrelated and dissimilar in morpholo- Onagraceae pollen. Host switches to Onagraceae gy, the viscin threads of Onagraceae pollen and by single clades of Perdita (Xerophasma )and the pollenkitt and spines of Asteraceae pollen both Hesperapis (Panurgomia ) do not entail modifi- provide an alternative to using nectar to bind the cations of scopal hairs (Table SII). However, for pollen grains together and to the scopae. both bee genera, host switches to Asteraceae are Although pollen types with spines and copious associated with modified scopal hairs. In Perdita, pollenkitt are effective at attaching to all but one member of the Asteraceae clade ex- and to each other, they apparently resist being hibits elaborate scopal hairs (corkscrew-shaped, packed together with nectar by bees. Spines seem wavy, or branched) that appear derived to both increase the amount of nectar required to (Danforth 1996, Table SII,Figure3). In contrast, pack individual grains together and decrease the moist transport of Asteraceae pollen occurs in four size and stability of the final pollen mass large, species-rich clades of Perdita (subgenus (Vaissière and Vinson 1994). In most instances, Pygoperdita and the Octomaculata , Ventralis , moist-transporting bees have difficulty packing, and Zonalis species groups within subgenus or even reject, pollen types with large spines and Perdita s.s. ), all of which contain species that copious pollenkitt (Linsley 1960; Stephen et al. specialize on a wide variety of other plant taxa 1969; Raine and Chittka 2007; Lunau et al. 2015). and have simple scopal hairs. The pattern is In some cases, removing the pollenkitt or bending repeated in Hesperapis , with both simple and the spines increases the ability of bees to pack branched scopal hairs found in Asteraceae spe- moistened pollen (Lunau et al. 2015). The hypoth- cialists, suggesting that more elaborate scopal esis that pollen is kept partially dry primarily hairs are recent adaptations for transporting glazed for transport purposes is supported by the fact that Asteraceae pollen. glazed-transporting Perdita whose nesting Evolution of pollen transport 469 biology has been studied (P. albipennis , 2007; Nilsson and Alves-dos-Santos 2009). The P. boharti , P. coreopsidis , P. graenicheri )still major exception, the genus Dasypoda ,transports shape the pollen provisions into uniformly moist- dry pollen on plumose scopal hairs and contains ened spheres but do so in the nest (Danforth 1989; many Asteraceae specialists (Celary 2002; Norden et al. 1992; Parker 1981). Michener 2007; Michez et al. 2008). The results The association of Asteraceae pollen with dry of our initial investigations suggest that the ques- or glazed pollen transport on elaborate scopal tion of the ancestral state of pollen transport and hairs is also found in other bee groups. The sub- its evolutionary trajectory be reopened; only ad- family Panurginae, which includes Perdita ,con- ditional systematic and behavioral studies will tains multiple genera with some species that trans- settle this issue. port dry or glazed asteraceous pollen (Rozen 1989; Michener 2007). Examples include the ge- ACKNOWLEDGMENTS nus , whose members transport dry Asteraceae pollen on wavy scopal hairs We thank Joe Wilson for informative discussion, (Münster-Swendsen 1970;Rozen1971), as well Terry Griswold, James Pitts, and various anonymous as some species of and reviewers for helpful comments on the manuscript, , which transport dry or glazed Brian Rozick and Harold Ikerd for curatorial help, Doug Asteraceae pollen on branched scopal hairs Yanega, Jaime Pawelek, and Glenn Hall for providing (Rozen 1967; Danforth 1996). Many apid bees specimens, and the USDA ARS Pollinating Insect Re- that transport dry pollen on elaborate scopal hairs search Unit for general support and access to the insect are strongly associated with Asteraceae pollen collection and facilities. This work is supported by a National Science Foundation Graduate Research Fel- collection (e.g., Melissodes , Svastra ), especially lowship under grant number DGE-1147384, a Utah compared to related groups that transport moist- State University Graduate Enhancement Award, and a ened pollen such as Eucera and Centris Utah State University Ecology Center Research Award. (Moldenke and Neff 1974; Eucera : Timberlake We acknowledge the support from the Microscopy Core 1969; Centris :Aguiaretal.2003; Roubik and Facility at Utah State University for the SEM work. Villanueva-Gutiérrez 2009). Specialization on Onagraceae pollen is also commonly associated with bee genera that transport dry pollen such as Authors' contribution ZP came up with the initial idea Andrena , Melissodes , Sphecodogastra , for the project. ZP and VT designed the project. ZP gath- Megachile ,andDiadasia (Thorp 1979). ered the data. ZP and VT wrote the manuscript Historically, internal or dry pollen transport has been thought to be the ancestral state in bees (Michener 1944;Jander1976; Roberts and Evolution convergente du mode de transport du pollen Vallespir 1978; Radchenko and Pesenko 1996; chez deux genres d’abeilles vaguement apparentés (Hy- Michener 2007). However, our results best fit a menoptera: Andrenidae and Melittidae) hypothesis of Perdita and Hesperapis switching Hesperapis Perdita from moist to dry or glazed pollen transport due to Apoidea / / / brosse à pollen the adhesive properties of pollen grains. This hy- Konvergente Evolution einer Pollentransportform in pothesis is strengthened by the absence of appar- zwei entfernt verwandten Bienengattungen (Hymenop- ent switches from dry to glazed or dry to moist tera: Andrenidae und Melittidae) and suggests a reconsideration of the evolutionary pathway of pollen transport in bees. 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